Sleep is important for good health. Frequent disturbances during sleep or sleep fragmentation can have severe consequences including day-time sleepiness (with the attendant possibility of motor-vehicle accidents), poor mentation, memory problems, depression and hypertension. For example, a person with nasal congestion may snore to a point that it disturbs that person's ability to sleep. Similarly, people with OSA are also likely to disturb their partner's sleep. One form of treatment for patients with OSA is continuous positive airway pressure (CPAP) applied by a flow generator such as a blower (compressor) via a connecting delivery hose with a patient interface. Such a pressure treatment may be adjusted in response to detected patient conditions such as apneas, snoring or hypopneas but generally maintains an approximately constant positive pressure during each breathing cycle of the patient. The positive pressure can prevent a collapse of the patient's airway during inspiration, thus preventing events such as snoring, apneas or hypopneas and their sequelae.
Respiratory treatment apparatus may include a flow generator, an air filter, a patient interface such as a mask or cannula, an air delivery conduit connecting the flow generator to the mask, various sensors and a microprocessor-based controller. The flow generator may include a servo-controlled motor and an impeller. The flow generator may also include a valve capable of discharging air to atmosphere as a means for altering the pressure delivered to the patient as an alternative to motor speed control. The sensors may measure, amongst other things, motor speed, gas volumetric flow rate and outlet pressure, such as with a pressure transducer, flow sensor or the like. The apparatus may optionally include a humidifier and/or heater elements in the path of the air delivery circuit. The controller may include data storage capacity with or without integrated data retrieval/transfer and display functions.
Positive airway pressure may be delivered in many forms. As previously mentioned, a CPAP treatment may maintain a treatment pressure across the inspiratory and expiratory levels of the patient's breathing cycle at an approximately constant level. Alternatively, pressure levels may be adjusted to change synchronously with the patient's breathing cycle. For example, pressure may be set at one level during inspiration and another lower level during expiration for patient comfort. Such a pressure treatment system may be referred to as bi-level. Alternatively, the pressure levels may be continuously adjusted to smoothly replicate changes in the patient's breathing cycle. A pressure setting during expiration lower than inspiration may generally be referred to as expiratory pressure relief. As described by Sullivan in U.S. Pat. No. 4,944,310, positive airway pressure treatments typically provide gas under pressures to the patient in the range of 4 to 15 cmH2O from the device and may involve flow rates of at about 120 liters/minute. Some of the air may escape via an end restriction and not be delivered to the patient. These pressure settings may also be adjusted based on the detection of conditions of the patient's airway or respiration. For example, treatment pressure may be increased in the detection of partial obstruction, apnea or snoring. In some cases, positive airway pressure may be adapted to provide ventilation support. For example, a patient's ventilatory needs may be supported on a breath-by-breath basis by automatically calculating a target ventilation and adjusting the pressure support generated by an apparatus, such as a bi-level pressure treatment apparatus, so as to achieve the target ventilation.
Other devices are known for providing respiratory tract therapy. For example, Schroeder et al. describes an apparatus for delivering heated and humidified air to the respiratory tract of a human patient in U.S. Pat. No. 7,314,046, which was filed on 8 Dec. 2000 and assigned to Vapotherm Inc. Similarly, Genger et al. discloses an anti-snoring device with a compressor and a nasal air cannula in U.S. Pat. No. 7,080,645, filed 21 Jul. 2003 and assigned to Seleon GmbH.
Respiratory treatment apparatus are sometimes provided with accessory components for comfort conditioning of the flow or pressurized air supplied by the flow generator. For example, the supplied air may be applied to a humidifier to humidify and warm the treatment gas prior to its delivery to a patient. Similarly, various heating elements can be connected with a delivery conduit to help in maintaining a particular temperature of the supplied gas as it is conducted to the patient from a supply unit or humidifier.
It may be desirable to develop these devices with improved design efficiencies.